AF 447 Thread No. 7

[roulishollandais]

PIO/APC

Thank You MachinBird to come on the PIO .

I elaborated in 1992 a method to get out from a DUTCH ROLL, and demonstrated it five times ago, on a MD83 simulator (Finnair, Helsinki, dec 1992...).
Nobody understood how I did that (counting seconds precisly with my free-fall experience, and resolving two differential equations by head computing the "response" I had to fly, and did it with full success.
That is much more that what a pilot learns to fly. But a dutch roll who is not finished near of the ground is extremely dangerous, and I attribute some of the past crashes (I did not find them in the Aistotel data base) to this.
With my method it has been possible to get out the dutch roll, in less then 30 seconds, with loss of height less then thousand feet, it is then possible,falling in the dutch roll at the outer marker, to go around and come back safely. It is quite possible to do that without to have the mind overloaded with the new task. The captain who tried to come out the similar dutch roll, had 6000 hrs on the plane, and going on the back right and left, struggled and lost 11 000 FT to bring the wings level and stable .

The dutch roll is a severe PIO in MachinBird/Aristotel classification.

I agree totally with JCJEANT that without enough formation, the first thing is "HANDS UP". But a minimum training must be given to any professionnal pilot to be able to idendify the problem (is it a stall, a spin, a dutch roll, a deepstall, a lazy eight, a dynamic looping, aso.. Only next is it possible to learn a better method that « hands up » to correct the situation . This method does not concern a unexperienced pilot landing a C152 (Aristotel !).

I agree with MachinBird that it is not enough to "just fly", even for a very good pilot. Flying must be adapted to the dynamic situation. I already posted about the fact that dutch roll is not a problem of ge/speed, but of what doing what at which moment, how long, aso.


How does the dutch roll happen ? (I shall not explain here the total theory of coming out of a dutch roll, only main ideas). It is a frequency resonance (f2=n.f1 ; n=1,2,3,4,5,etc.) between the normal action of the pilot (is he volounteer if nobody learned him that ?!!!) and the natural roll stability of the aircraft.

a- Some aircrafts have this aerodynamic problem, the manufacturer has to correct, it comes sometime on little details.

b - The yaw damper can fail (leak of hydraulic liquid on the electronic box, modifying the electric characteristics, or mechanical failure inside the yaw damper) (failure or sabotage)

c - Modification of the aircraft characteristics due to bad, or insuffisant maintenance.

d - Modification of the aircraft characteristics due to bad flying, without respects of the speed limitation (for example >250 KTS under FL 100 for some aircrafts) repeated day after day...

e - Bad certification, without fully verification that ALL tests have been done, with positive proofs of acceptability for all them

f - To engage the p/a may be enough to start it too (classical or FBW aircraft), and disengage the p/a may be enough in a FBW aircraft. The use of the a/p On or OFF must be done ready to surprise.

g - For ANY AIRCRAFT, so stable he is, hard turbulence can start an oscillation, and the PILOT achives that catastrophic.

h - Last but not least, for ANY AIRCRAFT, ICING SUDDENLY, or ICE GOING AWAY SUDDENLY, may significantly modify the aerodynamic caracteristics and begin the furious mouvement with or without the help of the pilot !



After 1992 I tried to explain that to my pilot colleagues, but NOBODY in my french aeronautical community including administration of civil aviation wanted to listen anithing about that, rejecting strangely mathematics...
.
I wrote to the french BEA, and got no response
From 199 to 1998 nobody asked me how I had done, or to teach my method….and i turned my back , desesperating about flight safety.
In 1998, I got informed that a friend of Michel Baroin died in 1987 as passenger with him in his Learjet crash (not in the Aristotel data base). I had been his flight instructor and what I did read from the crash made me suspect a dutch roll finishing in a deepstall. I decided to start again to speak about coming out from dutch roll. I wrote a book… but found no editor .
Worse, I phoned with the Learjet Instructor in Genève (CH) ... and he explained that they (he ?) had found their own "method" to try to come out from the funest dutch roll : "Faire des cisaillements sur le palonier" (sic) (Quickly shearing pedals) !!!
This extremely wrong and dangerous "method" has been used by the copilot on the flight AA587 in the wake turbulence over the Queens : THE RUDDER BROKE (Nov 12. 2001).
The NTSB started after some time a public enquiry, and found terrifying facts, about flying, and maintenance of airliners and cracks in the fin. Some newspapers wrote about that, from New York and London : I traduced them from english to french, and the second times I showed them, I got death threats... Aerodynamic is really dangerous !

Reading the Aristotel document I am effraid to discover we are still not ready to see the end of the PIO or PAO : Why do they mix helicopter and fixed wing aircraft ? Equations are different ; solutions also. Beautiful categorisation from 1 to 8, but it is just a normalisation. Why do they mix pitch and roll PIO ? Solutions are different. Coming with the phase is a bad entry : without frequency resonance the phases will be different at the next cycle (and no PIO). Aristotel says the first element for an aircraft pilot coupling (APC) is a unfavorable vehicle dynamics : that is not true. A stable aircraft like A330 seems to be, in some specific environment may get in a APC. The « mental mismatch of the pilot » ? generaly the pilot flies same manner as he has learned to fly WELL, but this manner is not adapted to the situation. Finaly the close loop wood be for Aristotel the third key element : When we fly an aircraft we are always in a CLOSE LOOP. Pilots have to learn that and understand that. Aerobatics was much better to learn that, than 200 hours on C177RG or Trinidad ! Aristotel uses four categories of APCs : 1-2 linear and quasilinear ; 3.transitions in the aerodynamic configurations 4. Elastic structural modes or biodynamical couplings : But oscillation is not linear… Air is not elastic … And fly training is not a bioreaction but a Pavlov repetition ; stop with psychologising human factor : the main human factor in dynamic systems, is that a human is essentially a « time constant » !


As the AF447 fin was found by the Brezilian in one piece I already imagined the AF447 fin has broken (see my first pprune's post) like the AA587's one, and I am wainting due arguments from the BEA that it did not happened.


However I often looked BEA#3' DFDR graphs, and oscillations : I cannot find the dutch roll regularity, but that does not mean it was not : We still are unknowing the detailed Airbus software design (management of interruptions, time constants, damping coefficients, system architectur, size of piles, Bode diagrams, aso). (We also do not know the exact description of the flight laws : industrial secret ! We learned here that even AB simulators ,used to qualify the pilots, do not use flight laws but discrete description of the aircraft coming from test flights. But in our endless question about the crew conversation we find no word of wrong heading, despite it changed... It is impossible having 10, 100, 1000 or 10000 hours on the logbook to say not a word of this change . The BEA'silence, once more does us doubtus : Was is a pilot in the aircraft ? If the tail broked, due to a crak or misflying, with or without dutch roll, had they an explosive depressurization ? I was wondering too the oscillations in what seems to be an unstable deeptstall : strange, but possible if the fin has already started to fly away.



I am really very very very happy to read MB today ! Now we are doing aeronautics